In recent years the number of mobile computing devices has increased dramatically, creating a demand for more advanced mobile and wireless services. Mobile e-mail, mobile social media services, multi-player gaming and call-following are examples of how new applications are emerging on mobile devices. In addition, users are beginning to seek applications that not only utilize their current location but also share that location information with others. Parents wish to keep track of their children, supervisors wish to track the location of the company's delivery vehicles, and a business traveler looks to find the nearest pharmacy to pick up a prescription. All of these examples require the individual to know their own current location or that of someone else.
Location-based services are an emerging area of mobile applications which leverage the ability of new devices to calculate their current geographic position and report that to a user or to a service. Some examples of these services include local weather, traffic updates, driving directions, child trackers, buddy finders and urban concierge services. To be able to provide such services mobile devices are more and more incorporating positioning technology. For instance, mobile devices may be equipped with Global Positioning System (GPS) receivers, which receive radio signals from dozens of orbiting satellites that are used as reference points. The receivers measure the time it takes for the signals to reach the receiver. After receiving signals from three or more GPS satellites the receiver can triangulate its position on the globe.
Despite the growth in positioning technologies, problems remain. For instance, it is difficult for a mobile device to remain continuously aware of its location. GPS receivers, for example, do not work where people spend most of their time; coverage in current systems is generally constrained to outdoor environments. In addition, GPS, as well as other positioning technologies such as cell tower triangulation and Wi-Fi location systems, are not sufficiently battery efficient to be used continuously.